Devices of the general type involved herein are known. See U.S. Pat. Nos. 2,930,613 and 3,438,626 wherein the ground engaging elements are integral with the associated pads. It is known from U.S. Pat. No. 3,108,802 to provide for pivotable movement between a pad and its ground engaging element. It is also known from U.S. Pat. No. 3,310,320 to provide a skate board with spherical ground engaging elements.